Aircraft starter control system

ABSTRACT

A control system for automatically closing a solenoid-operated air valve that supplies pressurized air to rotate an air turbine starter motor of an aircraft engine when the starter rotor reaches a predetermined rotational speed. The control system senses rotation of the starter rotor and produces a pulse train wherein each of the pulses generated has a duration which is a function of the rotational speed of the starter rotor and compares each pulse duration to a reference pulse which corresponds to a predetermined rotational speed of the starter rotor. When the duration of the rotor pulses decreases to a point where they are shorter in duration than a reference pulse, the supply of pressurized air is removed from the starter, thereby removing power from the starter at the predetermined speed.

United States Patent [191 Coman [451 May21, 1974 AIRCRAFT STARTER CONTROL SYSTEM Primary Examiner-G. R. Simmons [75] Inventor: William E. Coman, Newport, N.Y. t Agent or Cuoco;

ar 2 [73] Assignee: The Bendix Corporation, Teterboro,

[57 ABSTRACT [22] F'led: 1972 A control system for automatically closing a solenoid- [21] App]. N 233,196 operated air valve that supplies pressurized air to rotate an air turbine starter motor of an aircraft engine when the starter rotor reaches a predetermined rotag 290/38 290/ 17 21 3 tional speed. The control system senses rotation of the [58] d x 4 starter rotor and produces a pulse train wherein each m 0 earc 123/1 7 of the pulses generated has a duration which is a function of the rotational speed of the starter rotor and compares each pulse duration to a reference pulse [56] References which corresponds to a predetermined rotational UNITED STATES PATENTS speed of the starter rotor. When the duration of the 3.712.283 l/l973 Kiess 290/38 rotor pulses decreases to a point where they are 3,440,433 4/1969 Coman 290/38 shorter in duration than a reference pulse, the supply of pressurized air is removed from the starter, thereby armer eta 2,768,331 lO/l956 Cetrone 290/40 X ggg z power from the Starter at the predetermmed 3,452.210 6/1969 Gray et al. 290/38 I 24 Claims, 4 Drawing Figures 3 v PULSE esusrmon a I 5 PERMANENT FIXED DURATION MAGNET BISTABLE DZ COMPARATOR STARTER GENERATOR VARIABLE PULSE DURATION SOLENO) PATENTEDMAY 21 1974 SHEET 2 (IF 2 1 AIRCRAFT STARTER CONTROL SYSTEM BACKGROUND OF THE INVENTION The present invention relates to an aircraft starter control system of the type having a control circuit to de-energize the aircraft starter motor when the starter rotor has reached a predetermined speed.

Basically, the control system for an aircraft starter includes a device for sensing the rotational speed of the starter rotor and a control circuit that removes power to the starter solenoid once the aircraft engine has started, thereby preventing the starter rotor from being rotated at excessive speeds that would adversely affect the starter motor.

Present starter control systems sense the rotation of the starter rotor by inducing an electric potential in a winding of a magnetic pickup and passing the signal produced to a filter circuit. The filter circuit blocks all signals below a predetermined frequency. The output of the filter circuit is connected to a transistor switch which is turned OFF when the frequency of the input signal exceeds a predetermined value. The transistor switch is connected in series to an electrical power source and when the transistor switch is OFF, power to the starter is'removed. The disadvantage of this type of circuit is the filter network associated therewith, which is both bulky and expensive. Further, the response time of the control circuit is limited by the fact that it is responsive to a frequency, which is a plurality of pulses, rather than a pulse. An example of the aforementioned prior art control system can be found in US. Pat. No. 3,440,433 to W. E. Coman, entitled Aircraft Starter Control issued Apr. 22, 1969.

SUMMARY OF THE INVENTION This invention provides an aircraft starter control system that is smaller in size, less expensive and has a faster response time than prior art control systems.

The invention is an airraft starter control system characterized by a control circuit which is responsive to each revolution of the starter rotor and de-energizes the starter circuit when the starter rotor reaches a predetermined rate.

In one embodiment of the invention the control circuit comprises: a permanent magnet generator for generating a first pulse train wherein each of the pulses generated has a duration which is a function of the rotational speed of the starter rotor; a second pulse generator for generating a second pulse train wherein each of the pulses generated has a constant time duration that corresponds to a predetermined rotational speed of the starter rotor, at which the starter is to be deenergized; a comparator circuit for receiving the pulses from the first and second pulse generator and producing a first output signal when the duration of a pulse from the first pulse generator is shorter in duration than a pulse from the second pulse generator; and a transistorized switching circuit in combination with the power supplied to the starter, the transistorized circuit including a transistor switch which upon receipt of said first signal from said comparator becomes nonconductive to de-energize the circuit which supplies power to the starter.

Accordingly, it is an object of this invention to provide an improved control circuit for a control system for an aircraft starter motor.

It is another object of this invention to provide an automatic control circuit that de-energizes a starter motor of an aircraft engine from the engine when it reaches a predetermined rotational speed.

It is another object of this invention to provide a control circuit that includes a transistor switch that is polarity insensitive whereby the transistor switch operates regardless of how the transistor is connected to a power supply.

It is still another object of this invention to provide an improved aircraft starter control system that is more compact than prior control systems, and less expensive than prior control systems.

It is a further object of this invention to provide an aircraft starter control system which does not require bulky and expensive high pass signal filters.

It is still a further object of-this invention to provide an aircraft starter control system that utilizes integrated circuits and is vibration resistant.

Yet another object of this invention is to provide an aircraft starter control circuit that has a faster response time and better accuracy than previous aircraft control systems.

The above and other objects and features of the invention will become apparent from the following detailed description taken in conjunction with the accompanying drawings and claims which form a part of the specification.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. I is a block diagram of an aircraft starter control system.

FIG. 2 is a block diagram of a control circuit for an aircraft starter control system that utilizes the principles of this invention.

FIG. 3 is an alternate block diagram of a control circuit for an aircraft starter control system that utilizes the principles of this invention.

FIG. 4 is a schematic diagram of a control circuit shown in FIG. 3.

DETAILED DESCRIPTION OF THE DRAWINGS Referring now to the drawings, FIG. 1 illustrates an aircraft starter control system. In this system the control circuit senses the rotational speed of the starter rotor and transmits a signal to deenergize the power to the starter motor and/or starter solenoid when the rotational speed of the starter rotor has reached a predetermined speed. For purposes of this invention a signal may be either the presence of a current (voltage) or the absence of a current (voltage), depending on how one wishes to operate the circuit.

FIG. 2 illustrates how the control circuit reacts to pulses generated byrotation of the starter rotor. In this embodiment a permanent magnet generator 1 supplies impulses to a bistable 2 and an AND gate 9. The bistable device 2 initiates a pulse upon receipt of a first impulse from the permanent magnet generator 1 and terminates the pulse upon a second impulse from the permanent magnet generator I. The output of the bistable or flipflop device 2 is applied to a comparator 5 and to a pulse generator 3. The pulse generator 3 produces a pulse of fixed duration upon receipt of a pulse from the bistable 2. The duration of the pulse from the pulse generator 3 may be adjusted to correspond to any one of a plurality of speeds at which de-energization of the starter is desired. The comparator 5 receives pulses from the pulse generator 3 and from the bistable 2. The comparator then compares the two signals and provides an output signal to the AND gate 9 when the duration of a pulse from the bistable device 2 is greater than the duration of a pulse from the pulse generator 3. The AND gate 9, upon receipt of a signal D, from the permanent magnet generator 1 and the absence of an output current from the comparator (D, greater than D supplies a signal to power switch 6 to permit power to be supplied to the starter 8 from a power supply 7. As the speed of the starter rotor increases, the pulse duration from the bistable 2 will decrease. When there is a signal D, from the permanent magnet generator 1 and the duration of a pulse from the pulse D generator 3 is greater than the duration of a pulse D, from the bistable 2, the comparator 5 will not supply a signal to the AND gate 9 and no power will be supplied to the starter.

Noted on the block diagram shown in FIG. 2 are the symbols D, and D which correspond to the duration of a pulse from the bistable device 2 and pulse generator 3 respectively. D corresponds to a signal (voltage) supplied from the permanent magnet generator circuit 1. From FIG. 2 and the notations it can be seen that power will be supplied to the starter 8 when the duration of a pulse from the bistable 2 is greater than a pulse from the pulse generator 3 and a signal D is present at the AND gate 9. This condition is indicated by the solid line which indicates that the power switch 6 is ON when D, is greater than D, and signal D is present at the AND gate 9. Conversely, the starter 8 will be deenergized when the duration of a pulse D from the pulse'generator 3 is greater than the duration of a pulse D, from the bistable 2. This condition is indicated by the dotted line which indicates that the power switch is OFF when D is greater than D,.

FIG. 3 is also a block'diagram ofa control system that incorporates the principles of this invention. The symbols used on the lines connecting the blocks correspond to the following information: D, is the duration of a pulse from the bistable 2; D is the duration of a pulse from the pulse generator 3; D is the signal from the permanent magnet generator circuit which is preferably a voltage signal rather than a pulse signal. The numbers associated with the lines connecting blocks can be used together with the circuit shown in FIG. 4 to identify the signal connecting leads between each circuit.

When the starter rotor is rotating, the permanent magnet generator 1 supplies pulses to the bistable device 2 which in turn supplies pulses to the comparator 4 and pulses to trigger pulse generator 3. Comparator 4 compares the duration of the pulses from the pulse generator 3 to the duration of a pulse from the bistable 2 and produces an output signal when the duration of a pulse D, from the bistable has a duration greater than a pulse D from the pulse "generator 3. Comparator 5, upon receiving a signal from the comparator 4 and a signal from the permanent magnet generator 1, supplies an output signal to transistor switch 6, allowing transistor switch 6 to remain ON, thereby supplying power to the starter and starter solenoid. The absence of a signal from comparator 5, indicated by dotted line 501, causes transistor switch 6 to turn OFF, thereby deenergizing the starter and/or starter solenoid. The conditions necessary to de-energize the starter are indicated at the output of comparator 5, that is, that the duration of a pulse D from the pulse generator 3 be greater in duration than a pulse D, from the bistable 2 and there must be a signal from permanent magnet generator 1.

FIG. 4 is a schematic diagram of the block diagram shown'in FIG. 3. For clarity, portions of the circuitry have been outlined by dotted lines and identified as corresponding to the circuitry associated with the particular block shown in FIG. 3.

The permanent magnet generator circuit 1 includes a permanent magnet 101 which may be attached to the rotor shaft of the starter (not shown) to induce a voltage pulse in winding 102. Pulses from winding 102 are applied to a full wave rectifier bridge having diodes 11.'

The output of the bridge is attached to a circuit that includes capacitors 12 and 14, zener diode l3 and resistor 15 for smoothing out and regulating the rectified current from the bridge 10. The rectified current produced by the bridge 10 is supplied to zener diode 52 of comparator 5 through lead 101. The output of the bridge 10 that is smoothed by capacitors 12 and 14 is also supplied to a bistable device through resistors 19, 21 and lead 100. Transistor 17, in circuit relationship with capacitor 18 and resistor 16, is connected to one input of the bridge 10 and the negative output of the bridge 10. The transistor 17 shorts out the signal that flows through resistor 19 on'every half-cycle so that only one pulse is supplied to the bistable 2 for every revolution of the starter rotor. Therefore, in this arrangement the bistable will produce one pulse for every two revolutions of the starter rotor.

The bistable device 2 shown within the dotted lines is a solid state integrated circuit 22 that is capable of operating over a temperature range of -65F to 250F. The bistable 22 receives its input power from lead 23 and its input signals through lead from the permanent magnet generator circuit 1. The bistable 2 is a flipflop circuit that initiates a pulse upon receiving a first impulse from the permanent magnet generator circuit 1 and terminates such pulse on a second impulse from the permanent magnet generator 1. The bistable or flipflop device 22 supplies a trigger pulse to pulse generating circuit 3 through lead 200 and a complementary pulse to comparator 4 through lead 201.

The pulse generator circuit 3 includes resistors 31 and 32 and capacitor 33 which determine the duration of the pulses generated by the multivibrator circuit 30 which is an integrated circuit capable of operating over a temperature range of 65F to 250F. The resistors 31, 32 or capacitor 33 may be manually adjustable so that the duration of the pulses generated by the multivibrator circuit 30 can be adjusted to correspond to any fixed duration which further corresponds to a particular rotor speed.

Each time the multivibrator circuit 30 receives a pulse through lead 200 from the flipflop device 22, it produces an output pulse having a fixed duration determined by resistors 31 and 32 and capacitor 33. These pulses of the multivibrators circuit having constant duration are supplied through lead 300 to comparator circuit 4.

The comparator 4 includes an integrated circuit 40 that is capable of operating over a temperature range of 65F to 250F. The integrated circuit 40 produces an output signal through lead 400 and diode 42 to comparator circuit 5 upon receipt of a pulse from the flipflop device 22 that is greater in duration than a pulse supplied to the comparator 40 from the multivibrator 30. In the event that the duration of a pulse from the multivibrator 30 is greater than the duration of a pulse from the flipflop circuit 22, the comparator 40 does not provide an output signal through lead 400 and diode 42.

The second comparator 5 or AND gate includes a transistor switch 54 that is conductive upon receipt of a signal from the first comparator 4 through lead 400 and diode 42; a zener diode 52 which does not allow current to flow through the collector-emitter terminals of transistor 54 until there is a sufficient drive current available at the output of the bridge in the permanent magnet generator circuit; and a silicon-controlled rectifier 57 which has a signal supplied to the gate 59 thereof when transistor 54 is OFF, thereby allowing a current to flow through lead 501, diode 68, siliconcontrolled rectifier 57 and lead 500 which is the return to the negative side of the rectifier bridge 10. With current flowing through diode 68 a positive potential is de veloped between points B and A, with B being the positive terminal.

The function of zener diode 52 is to inhibit the action of silicon-controlled rectifier 57 by preventing current flow to gate 59 when the rotational speed of rotor 101 is very low. Under this condition the voltage available at lead 23 is insufficient to properly operate the logic elements and can cause a false shutdown signal from first comparator 4.

From the description of the second comparator 5 it is evident that the second comparator operates as a signal inverter. In other words, when'a signal is supplied to the second comparator 5 from the first comparator 4, no potential is developed across diode 68. However, when the input signal from the first comparator 4 through lead 400 and diode 42 is removed, the second comparator 5 produces an output signal in the form of a voltage developed across diode 68.

The transistor switch 6 is a transistorized switching network that includes a main switching transistor 66; signal amplifying transistors 62 and 64; zener diode 67; and a full wave rectifier bridge 60 that includes rectifiers 61 and 72. The input leads 68 and 69 to the bridge 60 also function as the output leads of the transistor switch 6.

The transistor switch does not require a rectifier bridge 60. However, the bridge 60 makes the transistor switch 66 polarity insensitive. In other words, regardless of the polarity of the signal applied to leads 68 and 69, transistor 66 will function.

When transistor 66 is ON there is a current path from lead 68, diode 61, transistor 66, diode 72 and lead 69, and coil 81 is energized by battery 82. When transistor 66 is OFF, current cannot flow between leads 68 and 69 and coil 81 is de-energized.

The transistors 62, 64 and 66 are arranged in combination with a bridge rectifier 60 so that when the current flows through the bridge from battery 82, transistor 66 is forward biased ON and transistors 62 and 64 are also conducting ON. Transistors 62, 64 and 66 remain ON when transistor 54 is ON which allows current to bypass diode 68 through lead 500 where it returns to the negative terminal of bridge rectifier 10. However, when transistor 54 is OFF, silicon-controlled rectifier 57 is gated ON generating a voltage across diode 68 that reverse biases transistor 62 which in turn turns OFF transistors 64 and 66.

The starter circuit 8 includes a source of d-c power, such as a battery 82, in series with a starter motor and- /or solenoid winding 81 which is in series with transistor 66 of the transistor switch 6. Therefore, when transistor 66 is conducting (ON), power is supplied to the coil 81 and when transistor switch 66 is nonconducting (OFF), power is removed from winding 81.

OPERATION In operation the aircraft starter control system operates as follows: certain aircraft engines have air turbine starter motors which are driven by a supply of pressurized air when a solenoid-operated control valve is opened. Consider now FIG. 4 which shows a winding 81 which corresponds to the solenoid valve. To supply pressurized air to a turbine starter motor, electrical energy, applied to the solenoid valve 81, operates to open the valve and supply pressurized air to rotate a turbine starter motor to start the engine (not shown). Current flowing through the coil 81 also flows through lead 68, diode 61, transistor 66, diode 72 and lead 69 to ground. Simultaneously, as the starter rotor begins to rotate, the permanent magnet 101 rotating past the coil 102 induces electrical impulses in the coil 102 that are rectified by bridge rectifier 10. During the initial stages of starting (low speeds) the duration of the pulses D, generated by the flipflop 22 is longer than the duration of the pulses D generated by the monostable multivibrator circuit 30 and therefore comparator 40 produces an output signal to keep transistor 54 ON. With transistor 54 ON, current from the output of the bridge 10 flows through lead 101, zener diode 52, the emittercollector electrodes of transistor 54, and back through lead 500 to the negative end of the bridge rectifier 10. With transistor 54 ON, no current flows through leads 501 and 502 and therefore no current flows through the silicon-controlled rectifier 57 or diode 68. Since ther is no current flow through diode 68 in the forward direction, transistors 62, 64 and 66 of the transistorized switch circuit are forward biased ON. As the rotational speed of the rotor increases, the duration of the pulses D generated by the flipflop 22 decreases until D is less than D and the solenoid air valve 81 is de-energized. More specifically, the de-energization of the solenoid 81 is accomplished as follows: as the speed of the starter rotor increases, the pulse rate of the permanent magnet alternator 1 increases, thereby shortening the duration of the pulses produced by the flipflop 22. When the duration of a pulse D becomes shorter than the duration D of a pulse from the multivibrator circuit 30, comparator 40 ceases to produce an output signal to transistor 54. When the comparator '40 ceases to provide an output signal to the transistor 54, transistor 54 turns OFF. This action allows current D to flow through lead 502, diode 55 and the gate electrode 59 of the silicon-controlled rectifier 57, turning the siliconcontrolled rectifier ON. Once the siliconcontrolled rectifier 57 is ON, a current flows from a bridge rectifier 10 through lead 101 out through lead 501, up through diode 68, through silicon-controlled rectifier 57, and then through the lead 500 to the negative end of the bridge 10. The current flowing through diode 68 acts to reverse bias transistor 62, turning transistor 62, 64 and 66 OFF. With transistor 66 OFF, current can no longer flow through winding 81 of the solenoid. With the winding of the solenoid de-energized, the source of pressurized air is isolated from the starter Coil 81 De-energized Coil 81 Energized Starter OFF Starter ON I. Pulse duration D, greater than pulse duration D, Pulse duration D greater than pulse duration D, and current signal D 2. Output signal from comparator 4 No output signal from comparator Transistor 54 OFF Zener diode 52 ON SCR 57 ON Diode 68 forward biased ON Transistors 62, 64, 66 OFF 3. Transistor 54 ON 4. Zcner diode 52 ON 5. SCR 57 OFF 6. Diode 68 reverse biased OFF 7. Transistors 62, 64, 66 ON In one satisfactorily operable system, the circuit shown in FIG. 4 included the following circuit elements which had the values or were of the types indicated as follows:

Rectifier bridge Diode ll Capacitor l2 Zener diode l3 l ampere, 50 volt l ampere, 50 volt 47 MFD, 35 volt Capacitor I4 220 MFD, 20 volt Resistor 100 ohms, 5 watt Resistor 16 5600 ohms, Va watt Transistor l7 Capacitor l8 Resistor 19 220 ohms, V4 watt Resistor 21 560 ohms, V4 watt Pulse generator 30 54l2l Resistor 31 l8000 ohms, V4 watt, 1'7: Resistor 32 24 ohms to 2000 ohms (select for precise speed setting, Vi watt Capacitor 33 0.10 MFD, 50 volt Flipflop 22 5473 (1%) (.l-K) Comparator 40 5473 (other A) Diode 42 lN400l Zener diode 52 lN474lA Resistor 53 470 ohms, V4 watt Transistor 54 IN 1 61 3 Diode 55 lN400l Resistor 56 I000 ohms, V4 watt Silicon-controlled rectifier 5 2N42l2 Resistor 58 Rectifier bridge 60 i000 ohms, V4 watt 25 ampere, 100 volt Rectifier 61 25 ampere, 100 volt Transistor 62 2N l 6l3 Resistor 63 15,000 ohms, V4 watt Transistor 64 2N325 lA Resistor 65 24 ohm, V4 watt Transistor 66 2N37l6 Zener diode 67 lN4754 Solenoid valve 8| Bendix Model 38E45 Storage battery 82 28 volt d-c While a preferred embodiment of the invention has been disclosed, it will be apparent to those skilled in the art that changes may be made to the invention as set forth in the appended claims, and in some cases certain features of the invention may be used to advantage without corresponding use of other features. For example, different types of semiconductors or solid state control devices may be substituted for the types illustrated. Further, a signal from a comparator may be considered as being either the presence or the absence of a voltage (current) which has an efiect on another stage of the circuit. Accordingly, it is intended that the illustrative and descriptive materials herein be used to illustrate the principles and not to limit the scope thereof.

Having described the invention, what is claimed is: l. A starter control system for automatically deenergizing a circuit, which supplies power to said starter, when the starter rotor reaches a predetermined rotational speed, said control system comprising:

means for generating a first pulse train wherein each of said pulses generated has a duration D which is a function of the rotational speed of said starter ro tor, said pulses decreasing in duration as the rotational speed of said rotor increases, said means for generating a first pulse train comprising: a permanent magnet generator; and a bistable circuit that initiates a pulse upon receiving a first impulse from said permanent magnet generator and terminates said pulse upon a second impulse from said permanent magnet generator; means for generating a second pulse train wherein each of said pulses generated has a constant time duration D; that corresponds to said predetermined rotational speed of said starter rotor at which said motor is to be de-energized; and switching means for de-energizing the circuit that supplies power to said starter when the duration D, of a pulse of said first pulse train is shorter than the duration D of a pulse of said second pulse train whereby the starter is automatically de-energized when said starter rotor reaches said predetermined rotational speed, said switching means comprising:

a first comparator circuit for receiving the pulses from said first pulse generator and said second pulse generator, said first comparator producing a first signal when the duration of a pulse from said first pulse generator is shorter in duration than a pulse from said second pulse generator; and

a transistorized switching circuit operable to remove electrical energy to said starter upon receipt of said first signal from said first comparator, circuit thereby de-energizing said starter.

2. The starter control system recited in claim 1 wherein said permanent magnet generator also includes means for rectifying the pulses generated by said permanent magnet generator.

3. The starter control system recited in claim 1 wherein said switching means for de-energizing the circuit that supplies electrical energy to said starter further comprises:

a second comparator having means for receiving a signal from said first comparator and means for receiving a signal from said permanent magnet generator, said second comparator operative to produce an output signal when it receives said first signal from said first comparator and a signal from said generator; and wherein said transistorized switching circuit conducts to apply electrical energy to said starter upon receipt of said output signal from said second comparator and is nonconductive to de-energize the circuit which supplies electrical energy to said starter in the absence of a first signal from said second comparator.

relationship with the output of said first compara-' tor;

a zener diode in circuit relationship with one other electrode of said first transistor and circuit relationship with the rectifying means of said permanent magnet generator; and

a silicon-controlled rectifier having its gate in electrical circuit relationship with said zener diode and one of its other electrodes in circuit relationship with the remaining electrode of said first transistor, said SCR being conductive when said first transistor is nonconductive and said zener diode is conductive, whereby said second comparator produces an output signal to turn off the transistorized switch and deenergize the starter. Y

5. In combination with an electric starting system for cranking an engine of the type having a source of electrical power, a starter motor, a solenoid and a mechanical switch for connecting the electrical power in circuit relationship with the solenoid, which, when energized,

couples the starter motor to the engine and connects the electrical power to the starter motor to crank the engine, wherein the improvement comprises:

switching means for automatically de-energizing said solenoid when said starter rotor has reached a predetermined rotational speed, said means for deenergizing said solenoid further including: means for generating a first pulse train wherein each of said pulses generated has a duration D, which is a function of the rotational speed of said starter rotor;

means for generating a second pulse train wherein each of said pulses generated has a constant time duration D that corresponds to said predetermined speed of said starter rotor; and

means for de-energizing said solenoid when the duration D, of a pulse of said first pulse train is shorter than the duration D of a pulse of said second pulse train whereby said starter motor is automatically decoupled from said engine when said starter rotor reaches said predetermined rotational speed.

6. The control system as recited in claim wherein said means for de-energizing said solenoid includes a transistor switch, in series electrical relationship with said solenoid, that is conducting ON when D is greater than D and is nonconducting OFF when D is less than D 7. The control system as recited in claim 5 wherein said means for generating said first pulse train includes a permanent magnet generator and a bistable multivibrator.

8. The control system as recited in claim 6 wherein said means for generating said first pulse train includes a permanent magnet generator and a bistable multivibrator.

9. The control system as recited in claim 6 including a full wave rectifier bridge having its output terminals connected to the collector and emitter electrodes of said transistor switch and its input terminals connected in series with said source of electrical power so that said transistor switch is operable regardless of the direction that current flows through said solenoid.

10. A control system for automatically closing a solenoid operated air valve that supplies pressurized air to rotate an air turbine starter motor of an engine, when the starter rotor reaches a predetermined rotational speed, said control system comprising:

means for sensing the rotational speed of said starter rotor and generating a first pulse train wherein each of said pulses generated has a duration D, which is a function of the rotational speed of said starter rotor; means for generating a second pulse train wherein each of said pulses generated has a constant time duration D that corresponds to said predetermined rotational speed of said starter rotor; and

means for closing the solenoid operated air valve when the duration D of a pulse of said first pulse train is shorter than the duration D of a pulse of said second pulse train whereby said supply of presusrized air is removed from said starter when said starter rotor reaches said predetermined rotational speed.

11. The control system as recited in claim 10 including a d-c power supply for supplying power to said solenoid and wherein said means for closing the solenoid operated air valve includes a transistor switch and a full wave rectifier bridge in circuit relationship with said power supply to control the power applied to said solenoid, said transistor switch having its emitter and collector terminals connected to the output of said bridge, said rectifier bridge having two input leads connectable in series to said dc power supply whereby said transistor switch is operable to permit current to flow into said solenoid from said d-c supply when either lead of said bridge is connected to the positive side of said d-c power supply and the remaining lead of said bridge is connected to said negative side of said d-c power supply.

12. A control system as recited in claim 10 wherein the means for generating a first pulse train is a permanent magnet generator.

13. The control system as recited in claim 10 wherein said means for generating a first pulse train includes a bistable circuit that initiates a pulse upon receiving a first impulse from said permanent magnet generator and terminates said pulse upon a second impulse from said generator.

14. The control system as recited in claim 12 wherein said means for generating a first pulse train includes a bistable circuit that initiates a pulse upon receiving a first impulse from said permanent magnet generator and terminates said pulse upon receiving a second impulse from said permanent magnet generator.

15. The control system as recited in claim 13 wherein said means for closing the solenoid operated air valve includes a comparator that compares the duration of a pulse from said bistable to the duration of a pulse from said second pulse train generator and provides an output signal when the duration of the pulse from said bistable is shorter than the duration of said pulse from said second pulse train generator.

16. The control system as recited in claim 14 wherein said means for closing the solenoid operated air valve includes a comparator that compares the duration of a pulse from said bistable to the duration of a pulse from said second pulse train generator and provides an output signal when the duration of the pulse from said bistable is shorter than the duration of said pulse from said second pulse train generator.

17. The control system as recited in claim 10 wherein said means for closing the solenoid operated air valve includes a transistorized switch in series electrical relationship with said solenoid and the power supplied to the solenoid so that when said transistorized switch is open, said solenoid is de-energized whereby said valve is closed thereby removing the supply of pressurized air that rotates said starter motor.

18. The control system as recited in claim 11 wherein said means for closing the solenoid operated air valve includes a transistorized switch in series electrical relationship with said solenoid and the power supplied to the solenoid so that when said transistorized switch is open, said solenoid is de-energized whereby said valve is closed thereby removing the supply of pressurized air that rotates said starter motor.

19. The control system as recited in claim 12 wherein said means for closing the solenoid operated air valve includes a transistorized switch in series electrical relationship with said solenoid and the power supplied to the solenoid so that when said transistorized switch is open, said solenoid is de-energized whereby said valve is closed thereby removing the supply of pressurized air that rotates said starter motor. I

20. The control system as recited in claim 14 wherein said means for closing the solenoid operated air valve includes a transistorized switch in series electrical relationship with said solenoid and the power supplied to the solenoid so that when said transistorized switch is open, said solenoid is de-energized whereby said valve is closed thereby removing the supply of pressurized air that rotates said starter motor.

21. The control system as recited in claim 15 wherein said means for closing the solenoid operated air valve includes a transistorized switch in series electrical relationship with said solenoid and the power supplied to the solenoid so that when said transistorized switch is open, said solenoid is de-energized whereby said valve is closed thereby removing the supply of pressurized air that rotates said starter motor.

22. A control system for de-energizing a circuit, said control system comprising:

a first circuit which includes:

a first source of electrical energy;

a reactive circuit element in series circuit relationship with said first source of electrical energy;

a first switch connected in series circuit relationship with said source of electrical energy and said reactive circuit element, said switch operable upon closing to apply electrical energy to said reactive circuit element; and

a transistor switch in series circuit relationship with said reactive circuit element, said transistor switch operable upon closing of said first switch to permit electrical energy to be supplied to said reactive circuit element, said transistor switch including a passive circuit element in circuit relationship with said transistor and having a voltage applied thereto from said first source upon closing of said first switch which forward biases said transistor so that said transistor is conductive a second circuit which includes:

an electromagnetic source of electrical energy separate from said first source of electrical energy for producing pulses which vary in duration as a function of a determinable parameter of said electromagnetic device, and including a pennanent magnet generator having a rotor and stator element, said generator generating electrical energy levels which are proportional to the rotational speed of the generator;

the reactive circuit element being the winding of an electromechanical device that controls power to a starter motor and said permanent magnet generator being mechanically linked to said starter motor;

and I a second solid state switching circuit in circuit relationship with said passive circuit element of said first circuit and said electromagnetic source of electrical energy, said second switch operable to apply a reverse voltage across said passive circuit element when said electromagnetic source of electrical energy produces a pulse having a predetermined duration whereby said first transistor switch is reverse biased rendering said first transistor switch nonconductive, thereby deenergizing said first circuit.

23. A control system as recited in claim 22 wherein the reactive circuit element is the winding of an electromechanical device and wherein said electromagnetic source of electrical energy is mechanically linked to said electromechanical device.

24. A starter control system for automatically deenergizing a circuit, which supplies power to said starter, when the starter rotor reaches a predetermined rotational speed, said control system comprising:

means for generating a first pulse train wherein each of said pulses generates has a duration D which is a function of the rotational speed of said starter rotor, said pulses decreasing in duration as the rotational speed of said rotor increases, said means for generating a first pulse train including: a permanent magnet generator;

means for generating a second pulse train wherein each of said pulses generated has a constant time duration D that corresponds to said predetermined rotational speed of said starter rotor at which said motor is to be de-energized; and

switching means for de-energizing the circuit that supplies power to said starter when the duration D, of a pulse of said first pulse train is shorter than the duration D of a pulse of said second pulse train whereby the starter is automatically de-energized when said starter rotor reaches said predetermined rotational speed, said switching means for deenergizing the circuit that supplies electrical energy to said starter comprising:

a transistorized switching circuit that includes at least one transistor, said transistor allowing electrical energy to be supplied to said starter in the conducting state and preventing electrical energy from being supplied to said starter in the nonconducting state; and g a comparator means for receiving pulses from said first pulse generator, pulses from said second pulse generator, and a voltage signal from said permanent magnet generator, said comparator means operable to produce an output signal upon receipt of a voltage signal of predetermined magnitude from said generator and a pulse from said first pulse generating means having a duration greater than a pulse from said second pulse generating means, said output signal coupled to said transistor switch to render said transistor conductive, whereby electrical energy is supplied to said starter when said transistor conducts and when said signal from said comparator means is removed, said transistor switch is nonconductive and said starter is deenergized. 

1. A starter control system for automatically de-energizing a circuit, which supplies power to said starter, when the starter rotor reaches a predetermined rotational speed, said control system comprising: means for generating a first pulse train wherein each of said pulses generated has a duration D1 which is a function of the rotational speed of said starter rotor, said pulses decreasing in duration as the rotational speed of said rotor increases, said means for generating a first pulse train comprising: a permanent magnet generator; and a bistable circuit that initiates a pulse upon receiving a first impulse from said permanent magnet generator and terminates said pulse upon a second impulse from said permanent magnet generator; means for generating a second pulse train wherein each of said pulses generated has a constant time duration D2 that corresponds to said predetermined rotational speed of said starter rotor at which said motor is to be de-energized; and switching means for de-energizing the circuit that supplies power to said starter when the duration D1 of a pulse of said first pulse train is shorter than the duration D2 of a pulse of said second pulse train whereby the starter is automatically de-energized when said starter rotor reaches said predetermined rotational speed, said switching means comprising: a first comparator circuit for receiving the pulses from said first pulse generator and said second pulse generator, said first comparator producing a first signal when the duration of a pulse from said first pulse generator is shorter in duration than a pulse from said second pulse generator; and a transistorized switching circuit operable to remove electrical energy to said starter upon receipt of said first signal from said first comparator, circuit thereby de-energizing said starter.
 2. The starter control system recited in Claim 1 wherein said permanent magnet generator also includes means for rectifying the pulses generated by said permanent magnet generator.
 3. The starter control system recited in claim 1 wherein said switching means for de-energizing the circuit that supplies electrical energy to said starter further comprises: a second comparator having means for receiving a signal from said first comparator and means for receiving a signal from said permanent magnet generator, said second comparator operative to produce an output signal when it receives said first signal from said first comparator and a signal from said generator; and wherein said transistorized switching circuit conducts to apply electrical energy to said starter upon receipt of said output signal from said second comparator and is nonconductive to de-energize the circuit which supplies electrical energy to said starter in the absence of a first signal from said second comparator.
 4. The starter control system recited in claim 3 wherein said second comparator comprises: a first transistor having its base in electrical circuit relationship with the output of said first comparator; a zener diode in circuit relationship with one other electrode of said first transistor and circuit relationship with the rectifying means of said permanent magnet generator; and a silicon-controlled rectifier having its gate in electrical circuit relationship with said zener diode and one of its other electrodes in circuit relationship with the remaining electrode of said first transistor, said SCR being conductive when said first transistor is nonconductive and said zener diode is conductive, whereby said second comparator produces an output signal to turn off the transistorized switch and deenergize the starter.
 5. In combination with an electric starting system for cranking an engine of the type having a source of electrical power, a starter motor, a solenoid and a mechanical switch for connecting the electrical power in circuit relationship with the solenoid, which, when energized, couples the starter motor to the engine and connects the electrical power to the starter motor to crank the engine, wherein the improvement comprises: switching means for automatically de-energizing said solenoid when said starter rotor has reached a predetermined rotational speed, said means for de-energizing said solenoid further including: means for generating a first pulse train wherein each of said pulses generated has a duration D1 which is a function of the rotational speed of said starter rotor; means for generating a second pulse train wherein each of said pulses generated has a constant time duration D2 that corresponds to said predetermined speed of said starter rotor; and means for de-energizing said solenoid when the duration D1 of a pulse of said first pulse train is shorter than the duration D2 of a pulse of said second pulse train whereby said starter motor is automatically decoupled from said engine when said starter rotor reaches said predetermined rotational speed.
 6. The control system as recited in claim 5 wherein said means for de-energizing said solenoid includes a transistor switch, in series electrical relationship with said solenoid, that is conducting ON when D1 is greater than D2 and is nonconducting OFF when D1 is less than D2.
 7. The control system as recited in claim 5 wherein said means for generating said first pulse train includes a permanent magnet generator and a bistable multivibrator.
 8. The control system as recited in claim 6 wherein said means for generating said first pulse train includes a permanent magnet generator and a bistable multivibrator.
 9. The control system as recited in claim 6 including a full wave rectifier bridge having its output terminals connected to the collector and emitter electrodes of said transistor switch and its input terminals connected in series with saId source of electrical power so that said transistor switch is operable regardless of the direction that current flows through said solenoid.
 10. A control system for automatically closing a solenoid operated air valve that supplies pressurized air to rotate an air turbine starter motor of an engine, when the starter rotor reaches a predetermined rotational speed, said control system comprising: means for sensing the rotational speed of said starter rotor and generating a first pulse train wherein each of said pulses generated has a duration D1 which is a function of the rotational speed of said starter rotor; means for generating a second pulse train wherein each of said pulses generated has a constant time duration D2 that corresponds to said predetermined rotational speed of said starter rotor; and means for closing the solenoid operated air valve when the duration D1 of a pulse of said first pulse train is shorter than the duration D2 of a pulse of said second pulse train whereby said supply of presusrized air is removed from said starter when said starter rotor reaches said predetermined rotational speed.
 11. The control system as recited in claim 10 including a d-c power supply for supplying power to said solenoid and wherein said means for closing the solenoid operated air valve includes a transistor switch and a full wave rectifier bridge in circuit relationship with said power supply to control the power applied to said solenoid, said transistor switch having its emitter and collector terminals connected to the output of said bridge, said rectifier bridge having two input leads connectable in series to said d-c power supply whereby said transistor switch is operable to permit current to flow into said solenoid from said d-c supply when either lead of said bridge is connected to the positive side of said d-c power supply and the remaining lead of said bridge is connected to said negative side of said d-c power supply.
 12. A control system as recited in claim 10 wherein the means for generating a first pulse train is a permanent magnet generator.
 13. The control system as recited in claim 10 wherein said means for generating a first pulse train includes a bistable circuit that initiates a pulse upon receiving a first impulse from said permanent magnet generator and terminates said pulse upon a second impulse from said generator.
 14. The control system as recited in claim 12 wherein said means for generating a first pulse train includes a bistable circuit that initiates a pulse upon receiving a first impulse from said permanent magnet generator and terminates said pulse upon receiving a second impulse from said permanent magnet generator.
 15. The control system as recited in claim 13 wherein said means for closing the solenoid operated air valve includes a comparator that compares the duration of a pulse from said bistable to the duration of a pulse from said second pulse train generator and provides an output signal when the duration of the pulse from said bistable is shorter than the duration of said pulse from said second pulse train generator.
 16. The control system as recited in claim 14 wherein said means for closing the solenoid operated air valve includes a comparator that compares the duration of a pulse from said bistable to the duration of a pulse from said second pulse train generator and provides an output signal when the duration of the pulse from said bistable is shorter than the duration of said pulse from said second pulse train generator.
 17. The control system as recited in claim 10 wherein said means for closing the solenoid operated air valve includes a transistorized switch in series electrical relationship with said solenoid and the power supplied to the solenoid so that when said transistorized switch is open, said solenoid is de-energized whereby said valve is closed thereby removing the supply of pressurized air that rotates said starter motor.
 18. The control system as rEcited in claim 11 wherein said means for closing the solenoid operated air valve includes a transistorized switch in series electrical relationship with said solenoid and the power supplied to the solenoid so that when said transistorized switch is open, said solenoid is de-energized whereby said valve is closed thereby removing the supply of pressurized air that rotates said starter motor.
 19. The control system as recited in claim 12 wherein said means for closing the solenoid operated air valve includes a transistorized switch in series electrical relationship with said solenoid and the power supplied to the solenoid so that when said transistorized switch is open, said solenoid is de-energized whereby said valve is closed thereby removing the supply of pressurized air that rotates said starter motor.
 20. The control system as recited in claim 14 wherein said means for closing the solenoid operated air valve includes a transistorized switch in series electrical relationship with said solenoid and the power supplied to the solenoid so that when said transistorized switch is open, said solenoid is de-energized whereby said valve is closed thereby removing the supply of pressurized air that rotates said starter motor.
 21. The control system as recited in claim 15 wherein said means for closing the solenoid operated air valve includes a transistorized switch in series electrical relationship with said solenoid and the power supplied to the solenoid so that when said transistorized switch is open, said solenoid is de-energized whereby said valve is closed thereby removing the supply of pressurized air that rotates said starter motor.
 22. A control system for de-energizing a circuit, said control system comprising: a first circuit which includes: a first source of electrical energy; a reactive circuit element in series circuit relationship with said first source of electrical energy; a first switch connected in series circuit relationship with said source of electrical energy and said reactive circuit element, said switch operable upon closing to apply electrical energy to said reactive circuit element; and a transistor switch in series circuit relationship with said reactive circuit element, said transistor switch operable upon closing of said first switch to permit electrical energy to be supplied to said reactive circuit element, said transistor switch including a passive circuit element in circuit relationship with said transistor and having a voltage applied thereto from said first source upon closing of said first switch which forward biases said transistor so that said transistor is conductive (ON); a second circuit which includes: an electromagnetic source of electrical energy separate from said first source of electrical energy for producing pulses which vary in duration as a function of a determinable parameter of said electromagnetic device, and including a permanent magnet generator having a rotor and stator element, said generator generating electrical energy levels which are proportional to the rotational speed of the generator; the reactive circuit element being the winding of an electromechanical device that controls power to a starter motor and said permanent magnet generator being mechanically linked to said starter motor; and a second solid state switching circuit in circuit relationship with said passive circuit element of said first circuit and said electromagnetic source of electrical energy, said second switch operable to apply a reverse voltage across said passive circuit element when said electromagnetic source of electrical energy produces a pulse having a predetermined duration whereby said first transistor switch is reverse biased rendering said first transistor switch nonconductive, thereby de-energizing said first circuit.
 23. A control system as recited in claim 22 wherein the reactive circuit element is the winding of an electromechanical device and wherein said electromagnetic source of electrical energy is mechanically linked to said electromechanical device.
 24. A starter control system for automatically de-energizing a circuit, which supplies power to said starter, when the starter rotor reaches a predetermined rotational speed, said control system comprising: means for generating a first pulse train wherein each of said pulses generates has a duration D1 which is a function of the rotational speed of said starter rotor, said pulses decreasing in duration as the rotational speed of said rotor increases, said means for generating a first pulse train including: a permanent magnet generator; means for generating a second pulse train wherein each of said pulses generated has a constant time duration D2 that corresponds to said predetermined rotational speed of said starter rotor at which said motor is to be de-energized; and switching means for de-energizing the circuit that supplies power to said starter when the duration D1 of a pulse of said first pulse train is shorter than the duration D2 of a pulse of said second pulse train whereby the starter is automatically de-energized when said starter rotor reaches said predetermined rotational speed, said switching means for de-energizing the circuit that supplies electrical energy to said starter comprising: a transistorized switching circuit that includes at least one transistor, said transistor allowing electrical energy to be supplied to said starter in the conducting state and preventing electrical energy from being supplied to said starter in the nonconducting state; and a comparator means for receiving pulses from said first pulse generator, pulses from said second pulse generator, and a voltage signal from said permanent magnet generator, said comparator means operable to produce an output signal upon receipt of a voltage signal of predetermined magnitude from said generator and a pulse from said first pulse generating means having a duration greater than a pulse from said second pulse generating means, said output signal coupled to said transistor switch to render said transistor conductive, whereby electrical energy is supplied to said starter when said transistor conducts and when said signal from said comparator means is removed, said transistor switch is nonconductive and said starter is de-energized. 